Auditory tone signal indications for flying



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ses.. ...d mkmam INVENTOR THEoo'oRE w. FORBES AT'TORN Y July 20, 1948. T. w. FORBES AUDITORY TONE SIGNAL INDICATIONS. FOR FLYING 3 Sheets-Sheet 3 Filed Aug. 21, 1947 ..om l 2m x6* lem v. oi Ism .En .oN n 6 .21 6.o .990 .3.. .owl a? o .2.. QN 52.6 .E1 md $3 E Y R E T w N N 0 R E E O v m n m A m ddr.. u m m www@ rimas .my zo, 194s AUDITORY TONE SIGNAL INDICATION S FOR FLYING Theodore W. Forbes, Cambridge, Mass., assigner to United States oi' America as represented by the Executive Secretary oi' the Oice o! Solentiilc Research and Development Application August 2l, 1947, Serial No. 769,951

3 Claims. (Ci. 117-811.)

This invention relates to indicators and more particularly to auditory tone signal indications for assisting a pilot in flying an airplane. An object of the invention is to provide auditory signal indications especially suited to "blind ying oi an airplane with a view to freeing the eyes oi.' the pilot lor other necessary duties, particularly at critical times.

An important feature ol the invention is a system of auditory tone signals which makes use of as many as three basic indications. The three indications are given by various characteristics oi a single signal, and the signal combination, therefore, diilers from auditory signals heretofore employed in which a number oi' separate tones are added together. The three-in-one signal of the invention has the advantage that it oilers less interference than does a signal composed of many different tones added together with radio and other communications which are necessary to the pilot. The signal oi the invention also has the advantage that all three of the indications are always heard together and there is less chance of one signal hlanhng out the other signals or attracting the pilot's attention to the exclusion oi' the other signals.

Another important characteristic oi the signal of the invention is that the indications are designed to be as simple and as self-explanatory as possible. This is achieved by making the characteristics of the auditory signal sound like the behavior of the airplane. Other combinations oi' signal characteristics may also be used although the one described herein has been tried out and found to be satisfactory and therefore constitutes a preferred embodiment of the invention.

Another important feature of the invention is an arrangement oi signals which are used to give turn," "bank" and air speed indications. The arrangement oi' signals may also be employed to give other indications such as indication of deviation from course, bank and horizontal attitudes of the airplane. or other similar information which may be desired. ther features will apgear from the following description ot the inven- In the accompanying drawings:

Figure l is a block diagram indicating functionally the apparatus o! the invention;

ml'igure 2 is a schematic diagram of the apparl i Figure 3 is a schematic diagram of a cycle divider; and

Figure 4 is stili another schematic diagram of a part of the apparatus.

Referring more in detail to the drawings, the basic signal heard when the plane is iiying straight and level is a "tone generated by the two signal oscillators of the signal generator shown in Fig. l. Each o! these oscillators generates a signal which has a "saw toothed or "spiked" wave i'orm, and the two oscillators are adjusted to the same frequency when the wings oi the plane are level. When the plane is not turning. the signal oscillator No. i (Fig. l) sends a signal to the right earphone or the pilot. and signal oscillator No. 2 sends a signal to the lett earphone. Under these circumstances. ii the left wing drops, the pitch of oscillator No. 2 drops accordingly, and it the leit wing rises above the horizontal. the pitch oi oscillator No. 2 rises accordingly. while that oi oscillator No. i remains fixed.

Control of the frequency oi oscillator No. 2 is obtained through the external bank control shown in Fig. i. The term external is used to indicate that the control potentiometer is outside of the signal unit and attached to the airplane's indieating instrument. In the case of the bank control, the control instrument may be a pendulum device, indicating in a similar way to the ball indicator oi the conventional airplane ball bank instrument. Thus in straight illying, when the left wing oi the airplane is above or below the right wing, the pitch of the tone in the lett ear is correspondingly heard to be higher or lower than the pitch in the right ear.

When the airplane begins to turn to right or lett oi a straight course. signal oscillator No. 2 is switched out oi' circuit and the signal from signal oscillator No. l is heard to swing or oscillate from one ear to the other. 111e relative bank indication of the bank-bank pendulum is now denoted by a tilt produced by means of a pitch variation during the apparent motion of the signal from side to side. This pitch variation is produced by potentiometer P: oi' the external bank control as shown in Pig. i. 'l'his potentiometer Pa was formerly out circuit but is thrown into circuit by the relay No. 2 when the turn indication takes control.

The pitch change is such that il' the left wing is toohighthepitchofthesignalwillbehigheron the left and lower on the right as the signal swings from one ear to the other. Thus in both straight llight and turning flight, the relative pitch of the signal to the two ears indicates position of the wingsoi the airplane on the corresponding sides. Furthermore, the pitch variatien is auch that the pilot do not have to discriminate absolute pitches but always a pitch which is relative to the pitch in the other ear. This is an important feature of the signal since the discrimination of the absolute pitch is diillcult for many people and has been shown to be unsatisfactory for auditory signal purposes.

ing to the right slowly. The intensity oi' the signal becomes suddenly strong in the left and weak in the right ear. It then becomes gradually stronger in the right and weaker in the left ear until it has become strong in the right and weak in the left. This gives the eiiect of motion of the signal from the left to the right side. This is accomplished by modulating the intensity of the signal to each ear separately in the two mixer stages of the modulator-and-mixer shown in Fig. i. i

The eil'ect of sudden movement to one side and gradual movement across to the other side is produced by the means of an oscillator giving a saw-toothed wave form o! very low frequency. The frequency employed here is in the range of one-fifth to eight cycles per second. The frequency oi this oscillator is important since frequencies which are too high are less effective in producing the sensation of motion of the signal when the pilot hears it in the earphones.

Control of the direction oi' motion and the irequency of the swing or motion of the signal is controlled by the external turn-control of Fig. l. This control was attached to the rate of turn indicator but may also be attached to the directional gyro. Switches SW1 and SW2 in Fig. i control the direction of the apparent motion of the signal and potentiometer C4 controls the rapidity oi' frequency of its sweep.

Relay No. 2 in Fig. l serves to disconnect signal oscillator No. 2 and to connect signal oscillator No. l to both mixer stage inputs. It also connects the turn-control and the bank-control to the output of the slow saw-toothed oscillator when the airplane starts to turn, thus causing the signal to sweep from side to side. ltelay No. l .acts as a reversing switch under the same circumstances, determining the direction ci the mo tion of signal and producing the appropriate pitch change in the bank signal. Both relays No. l and No. 2 are controlled by switches SW1 and BW: on y.the turn control.

Thealr speed signal is a "putt" or beep sound superimposed upon the basic tone signal.` 'l'he frequency of occurrence oi' this "putt" increases and decreases with the air speed when the air speed control potentiometer Pi of Fig. 1 is attached to an air speed meter. Alternatively, if desired, this signal could be used to indicate the horizontal attitude of the airplane. Since the "putt" sounds somewhat like the sound of a motor, a high speed "put (high rate of occurrence) is used to indicate high air speed and a` slow rate of occurrence low air speed In order to allow accurate judgment of Athe putt rate, a standard rate for comparison may be thrown in for one-third oi' each cycle of the slow saw-toothed oscillator. This is accomplished by the air-speed-comparison cycle-divider which is controlled by the saw-toothed oscillator out-` put wave'as shown in Fil. l.

Phase inverters are used in order to obtain the proper polarity of signals from the putt" generator and the saw-toothed oscillator. Audio amplifiers are' used following the saw-toothed oscillator in order to obtain the proper voltage for modulating the signal intensity in the mixer stages.

The general method oi obtaining these three signals consisting of a sweeping motion for turn, a "tilt" effect produced by pitch variation. and a "putt" sound superimposed on the basic tone signal, has now been described. The circuits by which these signals are achieved are shown in Figs. 2. 3 and 4. These circuits have been chosen for simplicity, but other circuits producing similar wave forms and similar modulations may be used.

The "put generator circuit consists of tubes Vi and Vn of Fig. 2 with their associated networks. The circuit represents a relaxation oscillator of a type well known to the art which produces a wave form of sharply peaked triangular shape. often called "spikes," rising from a ilat base line. An increased frequency oi' oscillation merely results in a closer spacing oi' these spikes" but with no essential Vchange oi' shape of the spikes" themselves. Frequency control is obtained by varying the bias on the control grid of V1 as shown in the diagram. The center tap connection between R4 and Rs provides a fixed comparison rate or frequency intermediate between the setting of potentiometers Re and R1. while potentiometer R: furnishes the variable Vputt" rate which is under control oi' the air speed indicator. Potentiometers Re and R1 furnish adjustments by which the maximum and the minimum putt" rate can be set to the desired frequency of occurrence. Relay RY1 is the relay in the cycle-divider which governs the relative time during which the comparison rate is heard.

The output oi' the "putt" generator oscillator is sent through Va and its associated networks which reverses the polarity of the signal.

Signal y oscillator No. 1 of Fig. 1 consists oi vacuum tubes V4 and Vn of Fig. 2 and their associated networks. Similarly signal oscillator No. 2 of Fig. l consists of vacuum tubes Vs and V1 of Fig. 2 and their networks. These signal oscillators are relaxation oscillators similar to the putt" generator. Potentiometers Re: and Ru furnish pitch settings for these two signal oscillators by which the pitch of the basic tone signal from cach oscillator can be set. Pitch control is obtained by a bias potential on the control gri 0f Vc and Vs.

The variable pitch control for oscillator No. 2 is furnished by Ras a potentiometer controlled by the bank pendulum. The variable pitch control for signal oscillator No. l, which causes the tiltl eil'ect in the moving signal. is obtained through the potential from the bank control potentiometer Ps of Fig. l. This is fed to the grid of V4 through resistor Rn.

The put or p" signal is led from the "pu generator and inverter through blocking oondensers Ca and Cu and resistors Rn and Rm to the control grid of v. and vi. The spiked shaped potentials from the putt generator cause a rapid frequency modulation of signal oscillators No. l and No. 2 simultaneously. thus superimposing the "putt upon the basic tone signals from these oscillators. Signal oscillators producing sinusoidal or other wave forms may be used providing they produce a tone which can be frequency modulated by the "putt" signal.

Figure 3 shows the circuit of the vacuum tube controlling the cycle diver relay RYi which throws in and out the comparison put rate frequency for the air speech signal. A potential from the saw-toothed oscillator of Fig. 4 is fed to the control grid of this vacuum tube through blocking condenser Ct and the potentiometer Rn. Bettings of potentiometers Ru and R41 determine the proportion of the saw-toothed cycle during which the comparison "put frequency is heard. This vacuum tube and relay circuit is of a type well known to the art.

The circuit for the modulator and mixer unit ofFig. 1 is shown in detail in Fig. 4. Tubes V1 and Va comprise the saw-toothed oscillator which is of a type well known to the art. Other circuits producing a saw-toothed wave form and a frequency or occurrence of the same range could be used in place of this circuit. Control of the frequency of occurrence of these saw-toothed potentlals is obtained by a bias potential on the control grid of V1. The basic frequency of oscillation is determined by the magnitude of condenser C1 and by the setting of the potentiometer R4. Rz and R: of Fig. 4 represent the center tapped potentiometer P4 in Fig. 1 which is moved by the turn indicator instrument. The

circuit is such that an increasing rate of turn to either side produces an increasing frequency of oscillation of the saw-toothed oscillator.

The potential wave of the saw-toothed oscillator is taken to the cycle divider at the point shown and also the inverter stage Va. The inverter is connected in "push-pull to the control grids of vacuum tubes V4 and Vs thus producing a saw-toothed potential of opposite polarity at blocking condensers Cs and C1.

The saw-toothed potential is transmitted through Cs and C1 to SW of Fig. 4 which represents the disconnecting and reversing relay connections in relays No. 1 and No. 2 of Fig. l. Thus this saw-toothed potential is connected across the resistor network Ras, Rao and Rsi. Rsi is a control potentiometer operated by the bank pendulum. When its wiper is centered, the opposite potentials may be balanced by means of R1 and Rss so that zero potential is sent to the signal oscillator and no pitch change results in signal oscillator No. 1. If however, the bank pendulum moves the wiper of Rsi to either side of center, a portion of the saw-toothed potential is imposed on the grid of signal oscillator No. 1. The dlrection of the rasulting pitch change corresponds to the position of the wings of the airplane, and the extent to which the control is moved off center controls the proportion of the saw-toothed signal sent to oscillator No. 1. Thus, as the control is moved farther oil! center. a greater pitch change in the desired direction is obtained.

The push-pull saw-toothed oscillator signal is also sent from switch SW to the oscillator grids of pentagrid mixer tubes Va and V1. Thus the positive phase of the signal causes an increased sensitivity of one tube and the negative phase causes a decreased sensitivity of the other tube. This sends increased intensity to one earphone and decreased intensity to the other earphone through the audio ampliners. At the initial peak of the saw-toothed modulating potential, one tube conducts maximally and the other is cut olf, midway through the modulating cycle both tubes conduct equally, and at the end of the cycle, the tube which conducted originally is cut on and the 6 other is conducting. Thus, the signal is caused to swing from one ear to the other.

The signals from signal oscillator No. i and signal oscillator No. 2 are fed to the pentagrid mixer tubes through relay No. i and relay No. 2 as shown in Fig. 1. These signals are sent to the control grid of pentagrid mixer tubes Vs and V1 through Rn and Rau of Fig. 4. Potentiometers Rss and Ru allow balancing of the signals which reach Vs and V1 to oifset any unbalance in the foregoing signal circuits. Thus the original signals to each ear will be equally loud. This is of importance in order that the modulation caused by saw-toothed oscillator may produce eective movement of the signal from one ear to the other.

Alternative inputs are provided through resistors Rsi and Raz in case it is desired to feed voice or radio signals into the mixers in such a way that they will be modulated and caused to swing from one ear to the other.

The outputs from the mixer tubes Vs and V1 are fed to two separate audio ampliiler channels, each of which supplies one earphone of the pilots headset.

While I have shown a preferred embodiment of my invention, it should be understood that various changes and modifications may be resorted to, in keeping with the spirit of the invention as defined by the appended claims.

I claim:

1. An auditory indicating device for flying an airplane comprising oscillators for producing a tone signal, means for separately conducting the tone signals to each of a pilots earphones, means for modulating separately and inversely signals to each earphone to indicate direction of turn of said airplane in a horizontal plane by producing a sound eifect in which a single tone signal appears to start from one side of the pilots head and to move toward the other side, said cycle being continuously repeated and moving in the same direction, means for reversing the direction of cycle of movement to indicate a reverse turn. and means for causing the tone signal to remain stationary thereby to indicate absence of turn of the airplane.

2. An auditory indicating device for flying an airplane comprising oscillators for producing a tone signal, means for separately conducting the tone signals to each of a pilots earphones, means for modulating separately and inversely signals to each earphone to indicate direction of turn of said airplane in a horizontal plane by producing a sound eect in which a single tone signal appears to start from one side oi the pilots head and to move toward the other side, said cycle being continuously repeated and moving in the same direction, means for reversing the direction of cycle of movement to indicate a reverse turn. means for causing the tone signal to remain stationary thereby to indicate absence of turn of the airplane, and means for continuously varying the pitch of the tone signal during the cycle in which it appears to swing from one side of the pilots head to the other side, thereby to indicate deviation of the lateral attitude of the airplane from the correct lateral attitude during a turn.

3. An auditory indicating device for flying an airplane comprising oscillators for producing a tone signal, means for separately conducting the tone signals to each of the pilots earphones, means for modulating separately and inversely signals to each earphone to indicate direction of 7 turn of said airplane in a horisontal plane by producing a sound eilect in which a single tone signal appears to start from one side of the pilot's head and to move toward the other side. said cycle being continuously repeated and moving in the same direction, means for reversing the direction ot cycle oi movement to indicate a reverse turn. means for causing the tone sianal to remain stationary thereby to indicate absence o! turn o! the airplanel means for continuously varying the pitch of the tone signal during the cycle in which it appears to swing from one side oi' the pi-lots head to the other side. thereby to indicate deviation of the lateral attitude during a turn, means for frequency modulating the said 8 signal oscillators by means oi' a potential ot spiked wave form. thus causing a rapid frequency change in the tone signal or signals and providing a continuous series ot staccato sounds forming a part o! the tone sllnals or siznal which appears to move. means responsive to change in longitudinal attitude or air speed o! the airplane for changing the rate oi occurrence oi' the staccato sounds. and means for maintaining rate of occurrence c! staccato sounds at a predetermined constant value during a portion only o! the said cycle of transfer oi' the signal from one side to the other in order to allow -low accurate Judgment of the signal. t 1

THEODORE W. FORBES.

Ccrtiiicate of Correction Patent No. 2,445,712.

July 2o, 194s.

THEODORE W. FORBES It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 13, strike out the word low; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of November, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uomm'issioner of Patents.

7 turn of said airplane in a horisontal plane by producing a sound eilect in which a single tone signal appears to start from one side of the pilot's head and to move toward the other side. said cycle being continuously repeated and moving in the same direction, means for reversing the direction ot cycle oi movement to indicate a reverse turn. means for causing the tone sianal to remain stationary thereby to indicate absence o! turn o! the airplanel means for continuously varying the pitch of the tone signal during the cycle in which it appears to swing from one side oi' the pi-lots head to the other side. thereby to indicate deviation of the lateral attitude during a turn, means for frequency modulating the said 8 signal oscillators by means oi' a potential ot spiked wave form. thus causing a rapid frequency change in the tone signal or signals and providing a continuous series ot staccato sounds forming a part o! the tone sllnals or siznal which appears to move. means responsive to change in longitudinal attitude or air speed o! the airplane for changing the rate oi occurrence oi' the staccato sounds. and means for maintaining rate of occurrence c! staccato sounds at a predetermined constant value during a portion only o! the said cycle of transfer oi' the signal from one side to the other in order to allow -low accurate Judgment of the signal. t 1

THEODORE W. FORBES.

Ccrtiiicate of Correction Patent No. 2,445,712.

July 2o, 194s.

THEODORE W. FORBES It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 13, strike out the word low; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of November, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uomm'issioner of Patents. 

